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However, early jet engines were too large to be worn by a person, so the only alternative was to use rockets.

Rockets work on a similar principle to jet engines, but instead of taking in air, the rocket uses self-contained chemical reactions to generate power.

You can read about 'Jetpacks' and much more in issue 58 of How It Works magazine, on sale now

The first proper attempt at a jetpack – the rocket belt – was invented by Wendell Moore in 1953, and flew using hydrogen peroxide rockets.

A tank of nitrogen gas forced hydrogen peroxide through a silver catalyst, causing it to rapidly break down into steam and oxygen.

The gas shot out of the nozzles at 33,280ft (1,000 metres) per second, producing over 280 pounds (125kg) of thrust.

This was powerful enough to lift the rocket belt and its wearer into the air for just over 20 seconds.

However, 70 per cent of the fuel in a rocket belt is required just to overcome the force of gravity, severely limiting flight time.

Adding more fuel made the rocket belt too heavy to fly, so even with improvements in design and weight reductions using lighter modern materials, hydrogen peroxide rocket packs still cannot fly for more than a minute.

One solution to the problem of heavy fuel is to attach the jetpack to a flexible supply hose, tethered to a fuel source on the ground.

While this seems impractical for a jetpack built for long-range transport, for recreational models, like the water-powered JetLev, this technique works well to extend airtime without weighing the pilot down.

The Martin Jetpack, illustrated here, is being heralded as the world's first commercial jetpack

The other alternative is to use a more efficient engine.

Advances in jet engine technology have allowed the production of units small enough to fit on a backpack, paving the way for the development of real jetpacks today.

The idea was trialled by the rocket belt’s inventor, Moore, in the late-Sixties using a custom-designed jet engine. Moore’s jet belt was capable of keeping someone airborne for up to 20 minutes, at speeds of 97 kilometres (60 miles) per hour.

However, the combination of a powerful jet, expensive, explosive fuel and a low-tech parachute system, made the jet belt impractical and pretty dangerous to fly.

One of the most impressive personal flying machines built using jet engines today is the jet wing, designed and piloted by Swiss inventor Yves Rossy.

This guide should give you some handy tips and pointers if you manage get your hands on a jetpack...

WHO IS YVES ROSSY?

A pilot turned inventor, Yves Rossy became the first man to fly using a jet-propelled wing.

TheSwiss-made machine began as a winged suit toglide through the air but Rossy soon beganexperimenting with engines.

At first, two model jetturbines were used, but this was upgraded to fouras it could only just maintain level flight.

Ahandheld throttle controls the jet wing and it canclimb at a rate of 330 metres (1,080 feet) perminute.

There have been more than 15 prototypes overten years of development.

The current model ispowered by four turbines and can reach speeds of300 kilometres (186 miles) per hour.

In 2008,Rossy crossed the English Channel and since then he hasflown with a Spitfire and across the Grand Canyon.

The semi-rigid carbon-fibre wing is just over 6.6 ft (2.2m) across and is attached to four modified kerosene-fuelled jet engines.

Jet engines are significantly more powerful than rockets so it takes just slight movements of the head, arms and shoulders to steer the wing.

However, this body control makes it impossible to launch the jet wing from the ground. Instead, the wing is deployed from a helicopter and the engines are used in a kind of powered freefall, allowing Rossy to fly through the air at an average speed in excess of 160 kilometres (100 miles) per hour.

'I had the idea to build a wing after discovering skydiving when I was 30,' says Rossy.

'I built this wing to make my dream a reality: to fly like a bird.

Here 'jetman' Yves Rossy is seen flying below a Spitfire plane back in 2012

'At the start, I could only glide. The next step was to motorise the wing, so I went to JetCat in Germany, world leader in model jet technology, and as my fi rst and most important sponsor theymade it possible to add power and engines.

THE DANGERS OF JETPACKS

Flammable fuelThe Jetman’s jet wing and the Martin Jetpack are both powered by explosive jet fuel typically used on larger aircraft, and so the pilot must wear a fire-retardant suit.

Noisy flightThe powerful fans keeping theMartin Jetpack and similarvehicles aloft in the air are soloud that the pilot is forced towear ear defenders to protecttheir hearing.

Midair failureIf a jetpack engine cuts outmidair, rapidly deployedballistic parachutes candrastically slow your descent,but these only work if you’rehigh enough from the ground.

Steam powerHydrogen peroxide rocketpacks use jets of steam andoxygen in order to getaround. Less explosive thanjet fuel but it puts the pilot ata great risk of burns.

Exhaust burnsNot only do pilots have towear fireproof suits, but theirfeet also need to be protectedfrom the high-temperaturegases being emitted fromthe engine exhaust.

'Flying with the jet wing is an unreal feeling, because normally you have a big thing – a plane – around you.

'I want to share my invention so we can eventually fly in formation with several wings.

'After that, I want to explore all the potential the wing has, because it’s enormous.

'I hope we are not too far [from mainstream jetpack flights] - my objective will be to share my passion.'

Another alternative to improve flight time is to abandon jet power altogether and turn to different means of becoming airborne.

Enter the Martin Jetpack; instead of using jet engines this relies on twin-ducted fans to generate lift.

Positioned on either side of the pilot, the two carbon Kevlar fans are driven by a bespoke V4 engine.

The
ducts are wider at the inlet than at the outlet, funnelling air through
at high speed, and producing enough thrust not only to lift the jetpack
and its pilot into the air, but also leaving an extra 50 kilograms (110
pounds) of thrust spare for rapid changes in altitude.

The Martin Jetpack can climb at nearly 800 ft (250metres) per minute.

The ducted fan design and petrol-powered
engine enable this jetpack to reach top speeds of 46
miles (74km) per hour, with a respectable flight time of half an hour,
allowing the pilot to travel distances of up to 19 miles (30km)
without needing to refuel.

The Martin jet-pack (pictured) is possibly the most similar in appearance to the 'Go Fast' jet-pack, despite being quite a bit larger, and relying on twin-ducted fans to generate lift. The petrol-powered jet-pack is less environmentally friendly than Jet PI's but can travel much further on a single tank of fuel

In the video above you can see the Martin Jetpack in action back in 2011

Interestingly, in unmanned testing, the Martin Jetpack has been able to reach altitudes of over 1,500 metres (5,000 feet).

Designing a jetpack is one thing, but ensuring that it’s safe to fly poses a whole new set of challenges.

Starting with bunny hops, the prototype flying machine is gradually refined and stabilised until it is able to take off safely.

Once airborne, the test vehicle is flown via remote control and constrained by a groundbasedtether, preventing any unexpected climb in altitude if the pilot loses control. If the jetpack passes these initial tests, tethered manned flights are then performed, allowing human operation to be tried in a safe environment.

Here the jetpack is compared to other more 'traditional' forms of air transport like planes and helicopters

Full-scale testing can then begin at higher altitudes and crash test dummies are used once again as the technology is refined.

Higher-altitude testing also allows for any safety features to be trialled.

The potential risks of fl ying a jetpack are high; the fuel is highly flammable, and an engine failure in midair could have catastrophic consequences.

Modern interpretations of the jetpack are built using high-tech composite materials and are packed with safety features.

During flight, pilots are kitted out in fire-retardant clothing and wear ear defenders to muffle the engine roar.

The Martin Jetpack is about as loud as standing in heavy traffic (around 95 decibels), although this is a signifi cant improvement over the rocket belt, which generated a deafening 130 decibels – equivalent to a pneumatic drill!

The flying machines themselves are also fitted with parachutes; for the jet wing this is necessary to land, while for the Martin Jetpack, it is used as an emergency backup.

The equipment is typically designed to be buoyant, ensuring the pilot is not dragged underwater should the jetpack land in water.

‘There are a number of challenges in building a jetpack,’ says CEO Peter Coker of Martin Aircraft, developer of the Martin Jetpack.

‘They include the design of a flight control system, the duct technology and the power-to-weight ratio of an engine.

‘We are now looking to commercialise the latest prototype [after] 33 years in development.

‘Jetpack theory is not simple, as shown by the time it has taken to develop the Martin Jetpack.

‘Regulations will probably restrict it initially but when “highways in the sky” are adopted by countries the full potential of the jetpack as a mode of transport can be fully realised.’

The company Jet Pack International is seen here testing out their jetpack design over Denver

Despite the progress over the last few years,there are still several limitations that stand in the way of a jetpack resembling the kind described by science fiction.

Jet fuel is heavy and expensive and, although ducted fans provide more efficient fuel consumption, at the moment they are much larger than the compact backpack most of us envisage.

Freedom of movement is a problem and the large duct casings that house the fans on the Martin Jetpack restrict its ability to move forward and backward at high speed.

Yves Rossy’s jet wing is much more responsive, but this comes at the cost of not being able to take off and land without a helicopter and a parachute, respectively, though this is something Rossy is looking to address, with research into taking off from the ground.

Despite not quite hitting the benchmark set by fictional jetpacks, the new technology has huge potential.

The military, search-and-rescue teams and emergency services in several countries have expressed interest in the Martin Jetpack.

It is quick, has a reasonable range and can reach areas inaccessible from the ground.

The units can also be controlled remotely, allowing jetpacks to enter areas too dangerous for humans, or to act as rescue drones, picking up a passenger and returning them to safety.

Ultimately though, the hope is that the Martin Jetpack will also be used for fun.

'Jetman' Yves Rossy flies over Rio de Janeiro, Brazil with a jetpack on 2 May 2012

The Martin Jetpack is seen here being shown off in front of crowds earlier this year

Until now, aviation authorities across the world haven’t had to deal with jetpacks, so no specific regulations are currently in place.

It is therefore up to local aviation authorities to set their own rules when the need arises.

In New Zealand, manned test flights of the prototype Martin Jetpack have been approved, but there are heavy restrictions.

The pilot must have a licence and can’t fly over 20ft (six metres) above the ground, or 25ft (7.6 metres) above water.

The finished jetpack, scheduled to hit the market by 2015, is expected to cost upward of £90,000 ($150,000).